KR20200132701A - A method for controlling defect density and texture in sputtered alxsc1-xn films - Google Patents

Abstract

An embodiment of the present invention relates to a deposition method. According to a part of embodiments of the present invention, disclosed is the method for sputter-depositing an additive-containing aluminum nitride film containing an additive element selected from Sc or Y, which comprises: a step of depositing a first layer of the additive-containing aluminum nitride film on a substrate disposed inside a chamber by using pulse-type DC reactive sputtering; and a step of depositing a second layer of the additive-containing aluminum nitride film on the first layer by using pulse-type DC reactive sputtering, wherein the second layer has the same composition as the first layer.

Description

How to control the defect density and texture of sputtered AlxSc1-xN film {A METHOD FOR CONTROLLING DEFECT DENSITY AND TEXTURE IN SPUTTERED ALXSC1-XN FILMS}

The present invention relates to a method for sputter deposition of an additive-containing aluminum nitride film. In particular, the present invention relates to a pulsed DC reactive sputtering method for depositing an aluminum nitride film containing an additive, such as an aluminum nitride film containing scandium or yttrium. The invention also relates to an additive-containing aluminum nitride film itself and a piezoelectric device comprising such a film.

Piezoelectric aluminum nitride (AlN) films are applied to RF resonator devices such as bulk acoustic wave (BAW) filters. Additive-containing aluminum nitride has been found to improve the device's electromechanical coupling efficiency (K _eff ) when compared to undoped aluminum nitride films. For example, by incorporating scandium into an alloy at the expense of aluminum, aluminum nitride containing additives in the form of Al _100-x Sc _x N with relatively high K _eff can be formed. Al _100-x when the composition in the form of Sc _x N represent, _x as a percentage, representing the _100-x and the _x value as a percentage is understood to be equal to _0.01x in stoichiometric chemical terms. In particular, c-axis oriented Al _100-x Sc _x N films are preferred for use in resonator devices because this orientation provides improved piezoelectric properties of the material.

There is a need to increase the electromechanical coupling factor in order to manufacture higher quality RF resonator devices. For example, increasing the amount of the additive element present in the additive-containing aluminum nitride can increase the electromechanical coupling coefficient (K _eff ). However, as the amount of the additive element present in the additive-containing aluminum nitride increases, there is a greater tendency for crystallographic defects to be formed. Crystallographic defects reduce the quality and crystallinity of the additive-containing aluminum nitride film. These crystal defects are piezoelectrically inert and thus adversely affect the electromechanical coupling coefficient of the additive-containing aluminum nitride film. That is, since the defect hardly has a piezoelectric reaction, piezoelectric bonding per unit volume of the film can be reduced. 1 shows an SEM image of crystal defects observed on an AlScN film prepared using a known deposition method. 2 shows a higher magnification SEM image of the crystal defect 20. In addition, these defects can be difficult to etch, can have a detrimental effect on the growth of subsequent layers, and consequently can affect subsequent processing steps.

Accordingly, there is a need to develop a method of increasing the amount of additive elements present in additive-containing aluminum nitride while maintaining acceptable defect density and crystallinity (or texture). Typically, a defect specification of less than 50 defects per 100 μm ² may be desirable to manufacture high quality devices. Typically, a texture specification of less than 2.0 deg FWHM may be desirable to produce high quality devices.

EP3153603 discloses a method of depositing an additive-containing aluminum nitride film by pulsed DC reactive sputtering. However, additional methods need to be developed to suppress the level of defects in the additive-containing aluminum nitride film, especially when the additive concentration is greater than about 8 At%. Accordingly, there is a need to further increase the additive element concentration (especially above about 8 At%) while suppressing defects and improving the film texture to a level acceptable for commercial manufacture of high quality RF resonator devices. An additional provision for ultimate commercialization is that the method must be able to be carried out in an economically viable manner.

The present invention, in at least some of its embodiments, seeks to address at least some of the aforementioned problems, desires and needs. The present invention, in at least some of its embodiments, provides a method of depositing an additive-containing aluminum nitride film having a low defect density, high electromechanical coupling coefficient (K _eff ) and suitable for use in resonator devices.

According to a first aspect of the present invention, there is a method of sputter-depositing an additive-containing aluminum nitride film containing an additive element selected from Sc or Y, the method comprising:

Depositing a first layer of an additive-containing aluminum nitride film on a substrate disposed in the chamber by pulsed DC reactive sputtering; And

Depositing a second layer of an additive-containing aluminum nitride film on the first layer by pulsed DC reactive sputtering, wherein the second layer has the same composition as the first layer.

Including, where

Depositing the first layer comprises introducing a gas or gas mixture into the chamber at a flow rate (sccm), wherein 87-100% of the flow rate (sccm) is a flow of nitrogen gas;

The step of depositing the second layer comprises introducing a gas mixture into the chamber at a flow rate (sccm), the gas mixture comprising nitrogen gas and an inert gas,

The percentage of nitrogen gas in the flow rate (sccm) used during the step of depositing the first layer is greater than the percentage of nitrogen gas in the flow rate (sccm) used during the step of depositing the second layer.

The first layer may be a seed layer. The first layer may provide a nucleation site for directional crystal growth of the second layer, for example in a c-axis orientation. Deposition of the first layer in a high nitrogen enriched atmosphere (e.g., 87-100%) allows high concentrations of additive elements to be incorporated into the aluminum nitride material while maintaining acceptable levels of crystal defects, crystallinity and texture. Turned out to be.

The additive element may be scandium.

The additive element is in the range of 0.5 At% to 40 At%, optionally in the range of 8 At% to 40 At%, optionally in the range of 10 At% to 35 At%, optionally in the range of 15 At% to 30 At%, or optionally 20 At % To 25 At%. The additive element may be present in an amount of> 8 At%,> 10 At%,> 15 At%,> 20 At%,> 25 At%. The additive element may be present in an amount of 40 At% or less. The additive element may be present in any combination of the upper and lower limits provided above. The method of the present invention can be particularly effective for depositing additive-containing aluminum nitride films with high concentrations of additive elements (e.g., greater than 8 At%) while maintaining acceptable levels of defect density, crystallinity and texture. have.

88% or more, 89% or more, 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more of the flow rate (sccm) used during the step of depositing the first layer , 97% or more, 98% or more, 99% or more, or 100% may be a flow of nitrogen gas. 90-100%, 94-100%, or optionally 98-100% of the flow rate (sccm) used during the step of depositing the first layer may be a flow of nitrogen gas. The flow rate (sccm) used during the step of depositing the first layer may include or consist of a flow of nitrogen gas and a flow of an inert gas such as argon.

The flow rate (sccm) used during the step of depositing the first layer can consist essentially of only a flow of nitrogen gas. Preferably, about 100% of the flow rate (sccm) during the step of depositing the first layer is a flow of nitrogen gas. That is, the flow rate (sccm) during the step of depositing the first layer is preferably only the flow of nitrogen gas. The flow rate (sccm) of nitrogen gas used in the step of depositing the first layer may be 50-500 sccm, optionally 60-250 sccm, optionally 100-200 sccm, or about 150 sccm. The flow rate (sccm) of nitrogen gas used in the step of depositing the first layer may be greater than 50 sccm, 60 sccm, 100 sccm, or 150 sccm. The flow rate (sccm) of nitrogen gas used in the step of depositing the first layer may be less than 500 sccm, 250 sccm, 200 sccm, or 150 sccm.

By using a nitrogen enriched or nitrogen-only atmosphere during the deposition of the first layer, the defect density, crystallinity and texture of the resulting additive-containing aluminum nitride film can be significantly improved compared to known methods. This effect is especially observed in nitrogen alone atmosphere. Without wishing to be bound by any theory or speculation, it is believed that depositing the first layer only in a nitrogen rich or nitrogen alone atmosphere has two advantageous effects. First, the number of argon atoms incorporated in the first layer is reduced. This reduces the potential source of atomic defects through which crystallographic defects can propagate through the additive-containing aluminum nitride film. Second, it is believed that the sputtering efficiency of the target is reduced because the target material is sputtered only by nitrogen rather than argon. Thus, fewer aluminum (or additive elements such as Sc or Y) atoms are sputtered from the target. It is believed that this increases the proportion of reactive nitrogen species in the deposition chamber so that reactive nitrogen species can be more advantageously deposited on the substrate. This leads to a more nitrogen-rich first layer (eg, an initial seed layer) on the substrate with fewer atomic point defects. As a result, there are few nucleation points where crystallographic defects grow, thus suppressing defect formation. In addition, there are a greater number of nucleation sites available for the c-axis nitrogen-terminated AlScN to grow in a well oriented texture mode. The c-axis Al _1-x Sc _x N growth can improve the piezoelectric properties of the additive-containing aluminum nitride film. Overall, this can reduce the number and density of defects in the additive-containing aluminum nitride film, and improve the electromechanical bonding efficiency of the film. This allows higher concentrations of additive elements to be present in the film while maintaining an acceptable level of defect density and texture.

The gas or gas mixture used during the step of depositing the first layer may include nitrogen gas and an inert gas. The inert gas may be a noble gas. Noble gases are understood to be gases of Group 18 of the Periodic Table of the Elements. The inert gas may be xenon, krypton or preferably argon. As the percentage of the inert gas used during the step of depositing the first layer increases to the level used in the known prior art, no advantageous effect of the present invention is observed.

The flow rate of the gas mixture used in the step of depositing the second layer may include about 83% nitrogen gas, and about 17% inert gas, such as argon. The flow rate (sccm) of nitrogen in the gas mixture used in the step of depositing the second layer is in the range of 50-250 sccm; Optionally in the range of 75-150 sccm; Or optionally about 83 sccm. The flow rate (sccm) of an inert gas such as argon used in the step of depositing the second layer is in the range of 8-50 sccm; Optionally in the range of 10-25 sccm; Or about 17 sccm. During the pulsed DC reactive sputtering process, the inert gas does not chemically react with the species. The inert gas may be a sputter gas. The inert gas of the gas mixture used during the step of depositing the second layer may be a noble gas such as xenon, krypton or preferably argon. Noble gases are understood to be gases of Group 18 of the Periodic Table of the Elements.

The ratio of nitrogen gas in the gas or gas mixture used during the step of depositing the first layer is usually higher than the ratio of nitrogen gas in the gas mixture used in the step of depositing the second layer. Without being bound by any theory or speculation, the use of a gas mixture containing a lower proportion of nitrogen gas for the deposition of the second layer can improve the sputtering efficiency and thus increase the deposition rate during the deposition of the second layer. I can make it.

The chamber may have a pressure of 2-6 mTorr, optionally about 4 mTorr, during the step of depositing the first layer.

The chamber may have a pressure of 1.5-7.5 mTorr, optionally about 3 mTorr, during the step of depositing the second layer.

The first layer can have a thickness of less than 70 nm, optionally less than 60 nm, optionally less than 50 nm, optionally less than 30 nm, optionally less than 25 nm, optionally less than 20 nm, or optionally about 17 nm.

The second layer can have a thickness that is at least 6 times thicker than the first layer, optionally at least 20 times thicker, optionally at least 25 times thicker, optionally at least 50 times thicker, or optionally about 60 times thicker than the first layer. have.

The additive-containing aluminum nitride film has a thickness of 0.3 μm or more; 0.6 μm or more; Or about 1 μm.

The additive-containing aluminum nitride film may have a thickness of 2 μm or less.

Depositing the first layer may be performed by applying an electric bias power to the substrate. The electrical bias power applied to the substrate during the step of depositing the first layer may be RF bias power. The electrical bias power applied to the substrate during the step of depositing the first layer may be greater than 200 W or greater than 250 W. The electrical bias power applied to the substrate during the step of depositing the first layer may be less than 350 W or less than 300 W. Applying a relatively high bias power (eg, greater than 200 W) to the substrate can cause the deposited additive-containing aluminum nitride film to have compressive stress. The inventors have found that a first layer having a compressive stress (eg, a seed layer) usually results in an additive-containing aluminum nitride film with a reduced defect density and improved texture and crystallinity.

The step of depositing the second layer may be performed without applying an electrical bias power to the substrate, or may be performed by applying an electrical bias power lower than the electrical bias power applied during the step of depositing the first layer to the substrate. The electrical bias power applied to the substrate during the step of depositing the second layer may be RF bias power. The electrical bias power applied during the step of depositing the second layer may be selected such that the total film stress (ie, the stress of the first and second layers) is about zero. The electrical bias power applied to the substrate during the step of depositing the second layer may be less than 100 W.

Pulsed DC reactive sputtering can be performed using a magnetron.

Pulsed DC reactive sputtering typically involves applying a pulse of DC power to a sputter target during sputter deposition. Pulsed DC reactive sputtering can be performed using a single target. The target may be a composite target formed from aluminum and additive elements. It is possible to use multiple targets, but it is less attractive economically.

The method may further include etching the surface of the substrate prior to depositing the first layer such that the first layer is deposited on the etched surface of the substrate.

The substrate may be a silicon substrate.

The substrate may comprise a metal layer, such as a molybdenum layer, onto which a first layer of an additive-containing aluminum nitride film is deposited. The method may further include depositing a metal layer on the substrate precursor. When a metal layer, such as a molybdenum layer, is deposited on the substrate precursor, the first layer is deposited on the metal layer. The step of depositing the metal layer may be performed prior to the step of etching the substrate.

According to a second aspect of the present invention, there is an aluminum nitride film containing an additive produced by the method according to the first aspect.

According to a third aspect of the invention, the additive element selected from Sc or Y is from 8 At% to 40 At%, optionally 10 At% to 35 At%, optionally 15 At% to 30 At%, or optionally 20 At% to 25 Contained in an amount in the range of At%; There are additive-containing aluminum nitride films with a defect density of less than 50 defects per 100 μm ² . The additive element may be present in an amount of> 8 At%,> 10 At%,> 15 At%,> 20 At%,> 25 At%. The additive element may be present in an amount of 40 At% or less. The additive element may be present in any combination of the upper and lower limits provided above.

According to a fourth aspect of the present invention, there is a piezoelectric device comprising an additive-containing aluminum nitride film according to one of the second or third aspect of the present invention.

The piezoelectric device may be a bulk acoustic wave (BAW) device.

The piezoelectric device may include first and second electrodes, and an additive-containing aluminum nitride film is disposed between the first and second electrodes.

While the invention has been described above, it extends to the foregoing features, or to any combination of the following description, drawings, and claims. For example, any feature disclosed in connection with one aspect of the invention can be combined with any feature of any other aspect of the invention.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.
1 is an SEM image showing an Al ₈₀ Sc ₂₀ N defect.
2 is an SEM image showing an Al ₈₀ Sc ₂₀ N defect.
3 is a TEM cross-sectional view of an Al ₈₀ Sc ₂₀ N defect.
4 is an illustration of a first layer of an AlScN film containing point defects.
5 is an illustration of a first layer of an AlScN film without point defects.
6 is an SEM image of an Al ₈₀ Sc ₂₀ N film including a 17 nm thick first layer having tensile stress.
7 is a SEM image of an Al ₈₀ Sc ₂₀ N film including a 17 nm thick first layer having compressive stress.
8 is a flow diagram illustrating the method of the present invention.

The inventors have found an advantageous process for sputter deposition of additive-containing aluminum nitride films. This method can help improve crystallinity and texture and reduce crystal defects in additive-containing aluminum nitride films. The additive-containing aluminum nitride film contains an additive element such as scandium (Sc) or yttrium (Y). The results presented below are related to scandium aluminum nitride (Al _1-x Sc _x N). However, this method is generally applicable to yttrium aluminum nitride (Al _1-x Y _x N).

The film is deposited by reactive sputtering, such as pulsed DC reactive sputtering. General details regarding devices that can be used in the present invention or that can be easily applied to use are described in the applicant's European patent applications EP2871259 and EP3153603, the entire contents of which are incorporated herein by reference.

The apparatus includes a substrate disposed in the chamber. The device further comprises a target. The target is a composite target formed from aluminum and additive elements. The composition of the target can determine the amount of additive elements contained in the sputter deposited film. It is possible to use multiple targets, but it is less attractive economically. Pulsed DC sputtering involves applying a pulse of DC power to a target during the deposition process.

In a first step, a first layer of an additive-containing aluminum nitride film is sputter deposited from a target on a substrate disposed in the chamber. The first layer is deposited by pulsed DC reactive sputtering. The first layer may be a seed layer. During the deposition of the first layer, a gas or gas mixture comprising nitrogen and optionally an inert gas such as argon is introduced into the chamber. The flow rate (sccm) of nitrogen gas during the first stage is 87-100% of the total gas flow rate (sccm) during the first stage. Optionally, the flow rate (sccm) of nitrogen gas during the first stage is 90-100%, 95-100%, 98-100% or about 100% of the total gas flow rate (sccm) during the first stage. Preferably, the gas or gas mixture consists of nitrogen gas only. The first layer typically has a thickness of less than about 70 nm, less than 60 nm, less than 50 nm, preferably less than 20 nm. In some embodiments, the first layer has a thickness of about 17 nm.

In the second step, a second layer of the additive-containing aluminum nitride film is then deposited on the first layer, for example on the initial seed layer. The deposition of the second layer may be bulk deposition. The second layer is deposited by pulsed DC reactive sputtering. During the deposition of the second layer, a second gas mixture comprising an inert gas such as nitrogen and argon is introduced into the chamber. Other inert gases such as xenon and krypton may be considered, but are less preferred because of their high cost. The ratio of nitrogen gas in the second gas mixture is usually less than the ratio of nitrogen gas in the first gas or gas mixture. In one embodiment, the flow rate of nitrogen gas is 83 sccm and the flow rate of argon gas is 17 sccm during deposition of the second layer. That is, the flow rate of nitrogen gas during the second step is about 83% of the total flow rate (sccm).

Typical deposition parameters for experiments on silicon substrates are presented in Table 1.

Table 1: Typical process parameters for AlScN deposition by a two-step process.

A 1 μm Al ₈₀ Sc ₂₀ N film was sputter deposited on a silicon substrate using a single target using the method described above. Table 2 shows how varying the proportion of nitrogen gas during the deposition of the first layer (i.e. the initial seed layer) affects the defect density (per 100 μm ² ) in the deposited 1 μm Al ₈₀ Sc ₂₀ N film. . Defect density was determined using scanning electron microscopy (SEM) images at 6,000 times magnification. Table 3 shows how changing the proportion of nitrogen gas during the deposition of the first layer (ie, the initial seed layer) affects the texture of the deposited Al ₈₀ Sc ₂₀ N film. X-ray diffraction (XRD) half-width (FWHM) measurements were used to determine the texture (or crystallinity) of the sample at the center, middle radius, and edge of the substrate. Lower FWHM values correspond to more crystalline films. Prior to the deposition process, the silicon substrate was subjected to a 2 minute degassing step at 350°C. Examples listed in the last column of Tables 2 and 3 included the additional step of subjecting the substrate to a 7.5 nm low bias etch step at 350° C. prior to the sputter deposition process. The SE-LTX module, available from SPTS Technologies Limited, is suitable for performing pre-treatment degassing and etching steps. The 1 μm Al ₈₀ Sc ₂₀ N film (shown in Tables 2 and 3) has a 17 nm thick compressible first layer (e.g., an initial seed layer) and a 983 nm second layer (e.g., a bulk layer). Include. The first layer was fabricated using a 300 W RF bias on a platen. The second layer was fabricated using an RF bias power selected to achieve zero stress across the film. That is, zero stress occurs across both the first and second layers. Typically, the bias applied to the platen during the second step is less than the bias applied to the platen during the first step. During the deposition of the second layer, the flow rate of nitrogen gas was 83 sccm and the flow rate of argon gas was 17 sccm.

Table 2: Defect density of 1 μm Al ₈₀ Sc ₂₀ N film on Si substrate at different percentages of nitrogen flow.

Table 3: XRD FWHM measurements of 1 μm Al ₈₀ Sc ₂₀ N films on Si substrates at different percentage nitrogen flows.

Table 2 shows that as the proportion of nitrogen gas (ie, flow percentage) increases, the density of defects at the edge, middle radius and center of the substrate decreases. Table 3 shows that as the proportion of nitrogen gas increases during the first (seed) step, the texture (0002) FWHM values tend to decrease at the edge, middle radius and center of the substrate. This effect is most pronounced when the gas used during the deposition of the first (seed) layer consists of nitrogen gas alone.

Without being bound by any theory or speculation, it is believed that crystallographic defects are caused by point defects such as atomic misalignment, misalignment, or vacancy. It is believed that most of the crystal defects in the AlScN film originate from the surface of the substrate material on which the AlScN film is grown. The resulting defects propagate through the film and can be observed on the film surface. 3 shows a TEM cross section of a crystal defect 30 in an Al ₈₀ Sc ₂₀ N film. The defect 30 propagates through the film. This defect is particularly pronounced in additive-containing aluminum nitride films in which the additive element (eg Sc or Y) is in an atomic concentration greater than about 8 At%. In the case of AlScN films, it is believed that the AlScN grains may be nitrogen or aluminum (scandium) terminated. Without wishing to be bound by any theory or speculation, it is believed that if a nitrogen layer is deposited as an initial atomic layer, crystallographic defects will form when other types of atoms are also incorporated into the initial atomic layer of nitrogen. 4 shows Al/Sc atoms 40 incorporated in the initial atomic layer of nitrogen to form point defects. This defect can propagate throughout the AlScN film. Also, without being bound by any theory or speculation, it is believed that increasing the proportion of nitrogen gas content during deposition of the first layer is advantageous for the deposition of a seed layer substantially free of point defects. For example, the initial atomic layer 50 may consist of substantially nitrogen alone (as shown in FIG. 5).

It is preferred to use a nitrogen rich or nitrogen alone atmosphere during the deposition of the first layer (ie, the initial seed layer). This can reduce the number and density of defects in the additive-containing aluminum nitride film, and improve the electromechanical bonding efficiency of the film. This allows higher concentrations of additive elements to be present in the film while maintaining an acceptable level of defect density and texture. Maintaining an acceptable level of defect density and texture in additive-containing aluminum nitride films with high concentrations (e.g.,> 8 At%) of additive elements results in a nitrogen gas fraction of about 83-87% in the first stage of deposition. It cannot be easily achieved using known methods such as the case of less than.

The Al ₈₀ Sc ₂₀ N films shown in Tables 2 and 3 were prepared so that the total stress of the Al ₈₀ Sc ₂₀ N film was zero by bulk deposition after depositing a compressible initial seed layer. The stress of the deposited film can be controlled by changing the substrate bias power. Table 4 shows how the XRD FWHM measurements of 1 μm Al ₈₀ Sc ₂₀ N films change when the first layer has tensile or compressive stress. The 1 μm Al ₈₀ Sc ₂₀ N film in Table 4 was formed by introducing nitrogen gas alone into the chamber during the deposition of the first layer. The first layer had a thickness of 17 nm and the second (bulk) layer had a thickness of 983 nm. 6 and 7 show SEM images of the Al ₈₀ Sc ₂₀ N surface for films deposited with tensile and compressible first layers, respectively. The Al ₈₀ Sc ₂₀ N film deposited with the compressible first layer exhibits lower defect density and improved texture compared to the Al ₈₀ Sc ₂₀ N film deposited with the tensile first layer.

Table 4: FWHM texture of 1 μm Al ₈₀ Sc ₂₀ N film on Si substrate with various stresses in the first layer.

The effects of the substrate material and surface condition were investigated. A 1 μm Al ₈₀ Sc ₂₀ N film was deposited on a molybdenum (Mo) coated substrate using a single composite target. Instead of Mo, other metal materials may be used as the coating material. The Mo-coated substrate was prepared according to the method shown in FIG. 8. The substrate precursor was initially degassed (step 802). The Mo coating was deposited on the degassed substrate precursor in the Mo deposition module (step 806). The Mo coating was etched using a low bias etch treatment (step 808). The substrate was then transferred to a sputter deposition module so that a two-step AlScN deposition process was performed (steps 810 and 812). The two-step AlScN deposition process includes i) depositing a first layer on the Mo-coated surface of the substrate in a nitrogen-rich or nitrogen-only atmosphere (step 810), and then ii) depositing a second layer on the first layer. (Ie, bulk deposition) (step 812). The process conditions used in steps 810 and 812 may be the same as or different from those described above with respect to other embodiments of the present invention.

Tables 5 and 6 show defect density and texture by changing the ratio of nitrogen gas during deposition of the first layer when depositing a 1 μm Al ₈₀ Sc ₂₀ N film on a molybdenum (Mo) coated substrate using the method of FIG. 8. Indicates how is changed.

Table 5: Defect density of 1 μm Al ₈₀ Sc ₂₀ N films on Mo substrates at different percentages of nitrogen flow.

Table 6: FWHM texture of 1 μm Al ₈₀ Sc ₂₀ N film on Si substrate at different percentage nitrogen flows.

Tables 5 and 6 show that the defect density for 1 μm Al ₈₀ Sc ₂₀ N on the Mo coated substrate can be reduced, and the texture can be improved by using nitrogen gas alone in a gaseous atmosphere during the deposition of the first layer. . In addition, conditioning the surface of the substrate by gentle etching prior to depositing AlScN can help suppress the formation of crystallographic defects and can improve the texture and crystallinity of the resulting AlScN film.

The influence of the thickness of the first layer on the defect density, crystallinity and texture was investigated. During the deposition of the first layer, a 1 μm Al ₈₀ Sc ₂₀ N film was prepared on the Mo-coated substrate using nitrogen gas alone. The Mo substrate was prepared according to the method of FIG. 8. The thickness of the first layer was varied and the texture of the resulting film was measured using XRD FWHM measurement. The results are presented in Table 7. The thinner first layer produced a more textured (ie, improved texture) Al ₈₀ Sc ₂₀ N film. This effect is more significant at the edge of the substrate. A suitable thickness of the first layer is usually less than 70 nm, less than 60 nm, less than 50 nm, less than 30 nm, less than 25 nm, or less than 20 nm.

Table 7: Influence of first layer thickness on Al ₈₀ Sc ₂₀ N texture.

In particular, it has been found that the combination of depositing a thin first layer in a nitrogen-rich or nitrogen-only atmosphere significantly reduces defect density and improves crystallinity and texture. This beneficial effect is also observed at high concentrations of additive elements. Accordingly, the method of the present invention is particularly suitable for depositing additive-containing aluminum nitride films having a high concentration of additive elements while maintaining acceptable levels of defect density, crystallinity and texture.

The above-described method can be used to deposit aluminum nitride films containing additives such as Al _1-x Sc _x N having various concentrations of additive elements. A 1 μm Al _1-x Sc _x N film was deposited on the base silicon substrate at 0 At%, 9 At%, 15 At% and 20 At%. An additive-containing aluminum nitride film was deposited from a single composite target. The amount of additive material in the deposited film was determined by the composition of the target. The first layer was deposited with an RF bias power of 200-350 W applied to the substrate. Nitrogen gas alone was introduced into the chamber during the deposition of the first layer. That is, the flow rate during the step of depositing the first layer was made of the flow of nitrogen gas. The thickness of the first layer was about 20 nm. The texture at the edge and center of the deposited film was measured, and the results are shown in Table 8.

Table 8: FWHM texture of 1 μm Al _1-x Sc _x N film on Si substrate with various seed composition

The present inventors believe that the step of depositing a first layer (e.g., an initial seed layer) of about 20 nm in which 100% of the flow rate (sccm) is a flow of nitrogen gas (N ₂ ) is It turns out that it has improved the texture. Improvements were observed for all additive element concentrations. This is particularly advantageous for high concentrations of additive elements, which lead to unacceptable levels of defects and poor texture by known conventional methods. This method allows acceptable levels of texture and defect density to be achieved for additive element concentrations greater than 8 At%, 9 At%, 10 At%, 15 At%, 20 At% and 25 At%.

Claims (23)

As a method of sputter deposition of an additive-containing aluminum nitride film containing an additive element selected from Sc or Y,
Depositing a first layer of an additive-containing aluminum nitride film on a substrate disposed in the chamber by pulsed DC reactive sputtering; And
Depositing a second layer of an additive-containing aluminum nitride film on the first layer by pulsed DC reactive sputtering, wherein the second layer has the same composition as the first layer.
Including, where,
Depositing the first layer comprises introducing a gas or gas mixture into the chamber at a flow rate (sccm), wherein 87-100% of the flow rate (sccm) is a flow of nitrogen gas;
The step of depositing the second layer comprises introducing a gas mixture into the chamber at a flow rate (sccm), the gas mixture comprising nitrogen gas and an inert gas,
An aluminum nitride film containing additives, wherein the percentage of nitrogen gas of the flow rate (sccm) used during the step of depositing the first layer is greater than the percentage of nitrogen gas of the flow rate (sccm) used during the step of depositing the second layer. Method of sputter deposition. The method of claim 1, wherein the additive element is scandium. The method of claim 1 or 2, wherein the additive element is in the range of 0.5 At% to 40 At%, optionally in the range of 8 At% to 40 At%, optionally in the range of 10 At% to 35 At%, optionally in the range of 15 At%. 30 At%, or optionally in an amount ranging from 20 At% to 25 At%. The method according to any one of claims 1 to 3, wherein 90-100%, optionally 94-100%, or optionally 98-100% of the flow rate (sccm) used during the step of depositing the first layer is of nitrogen gas. The way it is flow. The method of claim 4, wherein the flow rate (sccm) used during the step of depositing the first layer consists essentially of a flow of nitrogen gas alone. The method of any one of claims 1 to 5, wherein the flow of nitrogen gas used during the step of depositing the first layer is 50 to 500 sccm; Optionally 60 to 250 sccm; Optionally in the range of 100 to 200 sccm; Optionally about 150 sccm. 7. A method according to any of the preceding claims, wherein the gas or gas mixture used during the step of depositing the first layer comprises nitrogen gas and an inert gas such as argon. 8. The method of any of the preceding claims, wherein the chamber has a pressure in the range of 2-6 mTorr, optionally about 4 mTorr during the step of depositing the first layer. 9. The method of any one of the preceding claims, wherein the chamber has a pressure in the range of 1.5-7.5 mTorr, optionally about 3 mTorr during the step of depositing the second layer. The method of any one of claims 1 to 9, wherein the first layer is less than 70 nm, optionally less than 60 nm, optionally less than 50 nm, optionally less than 30 nm, optionally less than 25 nm, optionally less than 20 nm, or optionally about The method having a thickness of less than 17 nm. 11. The method of any one of claims 1 to 10, wherein the additive-containing aluminum nitride film is 0.3 μm or more; 0.6 μm or more; Or having a thickness of about 1 μm. 12. The method according to any one of claims 1 to 11, wherein the additive-containing aluminum nitride film has a thickness of 2 μm or less. 13. The method of any of the preceding claims, wherein depositing the first layer is performed by applying an electrical bias power to the substrate. The method of claim 9, wherein the step of depositing the second layer is performed without applying an electrical bias power to the substrate or by applying an electrical bias power lower than the electrical bias power applied during the step of depositing the first layer to the substrate. How to become. 15. The method of any of the preceding claims, further comprising etching the surface of the substrate prior to depositing the first layer such that the first layer is deposited on the etched surface of the substrate. 16. A method according to any of the preceding claims, wherein the substrate is a silicon substrate. 17. The method of any one of the preceding claims, wherein the substrate comprises a metal layer, such as a molybdenum layer, over which a first layer of an additive-containing aluminum nitride film is deposited. 15. The method of claim 14, further comprising depositing a metal layer on the substrate precursor. An additive-containing aluminum nitride film produced by the method according to any one of claims 1 to 18. Contains an additive element selected from Sc or Y in an amount ranging from 8 At% to 40 At%, optionally 10 At% to 35 At%, optionally 15 At% to 30 At%, or optionally 20 At% to 25 At%, ; Additive-containing aluminum nitride film with a defect density of less than 50 defects per 100 μm ² . A piezoelectric device comprising an additive-containing aluminum nitride film according to claim 18 or 19. The piezoelectric device according to claim 20, which is a bulk acoustic wave (BAW) device. The piezoelectric device according to claim 21, comprising first and second electrodes, wherein an additive-containing aluminum nitride film is disposed between the first and second electrodes.

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